Apparatus for producing alternating currents



Oct. 16, 1945. Q 5 2,386,811

APPARATUS FOR PRODUCING ALTERNATING CURRENTS Filed Feb. 10, 1942 6 Sheets-Sheet 1 AUTO-TRANSFORMER FIG INVENTOR HOWARD I. MORRFS ATTORNEY 0d. 16, 1945. o s 2,386,811

APPARATUS FOR PRODUCING ALTEiRNATING CURRENTS Filed Feb. 10, 1942 6 Sheets-Sheet 2 AUTO -TRAN$FORMER INVENTOR HQWARD I. MORRVS b 3.01m ATTORNEY Oct. 16, 1945. H. MORRIS 2,386,811

APPARATUS FOR PRODUCING ALTERNATING CURRENTS Filed Feb. 10, 1942 6 Sheets-Sheet 3 INVENTOR YHOWARD I. MORFUS ATTORNEY Oct. 16, 1945. H. 1. MORRIS APPARATUS FOR PRODUCING ALTERNATING CURRENTS Filed Feb. 10, 1942 6 Sheets-Sheet 4 INVENTOR B HOWARD I. MOQRB j /Wwa/ ATTORNEY Oct. 16, 1945. H. l. MORRIS APPARATUS FOR PRODUCING ALTERNATING CURRENTS Filed Feb. 10, 1942 6 Sheets-Sheet 5 FIG-ll FIG. \1

INVENTOR HOWARD I. MoRms j fivw ATTORNEY Oct. 16, 1945. H. l. MORRIS 2,386,811

APPARATUS FOR PRODUCING ALTERNATING CURRENTS Filed Feb. 10,. 1942 6 Sheets-Sheet 6 IN V EN TOR. HOWARD I. M ORRIS BY u/mm ATTORNEY interval incident to the Patented Oct. 16, 1945 APPARATUS FOR PRODUCING ALTERNATING CURRENTS Howard I. Morris, Lakewood, Ohio, asslgnor of one-third to Carl M. Yoder and one-third to Harvey 0. Yoder, both of Lakewood, Ohio Application February 10, 1942, Serial No. 430,232

8 Claims.

This invention relates to a method of and apparatus for producing alternating current having any desired frequency and capacity and iiivolving characterizing advantages to obtain improved useful results. The resulting current may be employed for effecting resistance welding operations, one example consisting in the use of rotatable electrodes engaging moving preformed pipe to weld the seam thereof; but as the produced current may be employed for other purposes, the herein described and illustrated application is merely descriptive and not intended to be in limitation of the invention.

In performing welding operations it is important to provide a uniform continuous weld throughout the length of the work, to avoid weakness. This condition has heretofore only been accomplished, so far as I am aware, by the use of direct current. However, as the cost of a D. 0. generator of the type and construction capable of supplying the low voltages such as used for resistance welding operations, is relatively high, and as alternating current is, in most instances, readily available, it has become more or less the standard practice in welding to use alternating current; but due to the reversal of flow or surges of opposite polarity incident to the latter type of current, the welding of the work takes place only during each surge of current, as no current flow to and through the work takes place during the changes in polarity. As a result, spacing occurs between the welded portions of the work, this condition being known as stitch weld," as shown herein in Fig. 9, which illustrates a weld effected by a 60 cycle alternating current. While in the useof A. C. of higher frequency, both the length of the welded portions or stitches and the spacing therebetween are proportionately reduced, a uniform, continuous weld is not attained. It will therefore be apparent that if each alternation of one polarity can be maintained at substantially maximum voltage and current throughout a major portion of the alternation and the time change from maximum voltage and current of one polarity to maximum voltage and current of opposite polarity can be reduced to a minimum, those portions of the metal which are fused during current flow through the work, will merge to produce a continuous weld of substantially uniform molecular character and thereby eliminate a stitched condition. Furthermore, in apparatus heretofore used for welding with alternating current having a high frequency inefficiency has been experienced due to the impedance in the circuit effected or produced by the reactance therein, which reactance is prortional to the frequency of the current.

One object of the invention is to provide an improved method of producing alternating current having a predetermined frequency, wherein the time interval in the change from maximum positive polarity to maximum negative polarity and vice versa is reduced to a minimum in each cycle.

Another object of the invention is to produce an alternating current of a predetermined frequenc in which the alternations reach maximum strength in the least possible length of time and remain substantially at the maximum strength for the greatest possible length of time in each cycle.

Another object of the invention is to produce alternating current having a predetermined frequency wherein the changes in polarity in each cycle are effected at the speed of an alternating current of higher frequency whereby the alternations between polarity changes are sustained at substantially maximum value.

Another object of the invention is to provide an improved method of producing alternating current by supplying alternating current at a predetermined frequency and superimposing thereon an alternating current of the same frequency, but having a plurality of pulsations of high acceleration of the same polarity in each alternation, whereby the resultant alternating current has a sustained peak value in the current alternations in each cycle and the time interval in the change from peak value of the positive polarity to peak value of negative polarity in each cycle is materially reduced.

Another object of this invention is to produce an alternating current of a predetermined frequency, in which the time of transition from one alternation to the next is of the speed of an alternating current of a higher frequency.

Another object of the invention is to provide an improved process of welding wherein is produced an alternating welding current capable of effecting a substantially uniform continuous weld throughout the length of the work.

Another object of the invention is to provide an improved process of and apparatus for producing from separately supplied alternating currents, one having a predetermined frequency, and the other having a plurality of surges of the same polarity occurring during the same time interval and of the same polarity as that of one alternation of the first mentioned supplied alternating current, an alternating current wherein substantially maximum voltage and current in each positive and negative alternation is sustained between the surges of the second named supplied current.

A further object of the, invention is to provide an improved process of resistance welding by alternating current wherein the time interval between changes from maximum voltage and current of one polarity to maximum voltage and current of opposite polarity is reduced to a minimum, whereby the duration of current flow to the electrodes in successive alterations is efiective to substantially uniformly weld the work throughout its length.

Another object of the invention is to provide an improved alternating current generator in which the poles on the stator and rotor are related to produce alternating current having a plurality of positive surges of the same polarity and negative surges of the same polarity in each cycle thereof.

Another object of the invention is to provide an improved welding apparatus which isrelatively simple in construction and economical to instalL- Other objects of the invention will be apparent to those skilled in the art to which my invention relates from the following description taken in connection with the accompanying drawings, wherein Fig. 1 is a diagrammatic view of apparatus embodying my invention and capable of carrying out my improved process.

Figs. 1a, 2, 2a, 3, 4 and 5 are diagrammatic views showing modified forms of construction.

Fig. 6 is a diagram showing two curves 1: and b representing the supplied alternating currents and a third curve 0 representing the resulting current produced therefrom by my process and apparatus.

Fig. 7 is a sectional view of a generator involving my invention and adapted for use in carrying my process; this view being a section on the line 3-1 of Fig. 8.

Fig. 8 is a section on the line 88 of Fig. 7.

Fig. 9 is a fragmentary view of a portion of a pipe, parts being broken away to show the seam weld effected by 60 cycle alternating current.

Fig. 10 is a view similar to Fig. 9 showing a weld effected by alternating current as produced by my process and apparatus.

Fig. 11 is a view, similar to Fig. 8, but showing a modified form of construction.

Fig. 12 is a section on the line I2l2 of Fig. 11.

Fig. 13 is a diagram showing two curves a and b representing the supplied alternating currents, where one thereof is supplied by the generator shown in Figs. 11 and 12, and curve 0 representing the resulting alternating current.

Fig. 14 is a developed view of the stator and rotor of the generator shown in Figs. '7 and 8.

Fig. 15 is a developed view of the stator and rotor of the generator shown in Figs. 11 and 12.

In the drawings, I indicates as an entirety (diagrammatically) an apparatus for welding work, which, for illustratitve purposes, consists of a pipe A the seam edges of which are to be welded. The apparatus comprises a pair of electrodes 2, 2a, and a transformer 3, having the terminals of its secondary winding connected respectively to the electrodes 2, 2a; the primary winding of the transformer being supplied with alternating current of the desired voltage, as later set forth, by leads 4, id.

The welding apparatus I may be of any preferred form of construction. The apparatus illustrated diagrammatically herein is shown in my co-pending application Serial No. 321,745, filed March l, 1940, (now Letters Patent No. 2,283,941, dated May 26, 1942) the electrodes and transformer being mounted for rotation as a unit and the current being supplied'to the primary winding of the latter through collecting rings 5. No claim is made herein to the construction of the welding apparatus i. 6 indicates an auto 2,886,811 transformer as illustrating one way whereby the voltage supplied to the transformer 3 may be suitably regulated.

I, 8, indicate sources of supply of single phase alternating current, wherein one has a plurality of pulsations of the same polarity in each alternation synchronized with alternations of the same polarity in the other supplied current, as later set forth. The source of supply I is shown as consisting of the mains 4, 4a, leading from an. outside supply station, whereas the source of supply 8 consists of leads 8a, 8b, to which is supplied from a suitable source alternating current wherein each alternation consists of a plurality of pulsations or surges of the same polarity. By preference the A. C. supply 8 consists of a generator, indicated as an entirety at 9, constructed to generate alternating current, each alternation of which consists of a plurality of pulsations of the same polarity synchronized with and effected in the same time interval of each alternation of the same polarity in th current supplied by source I. For example, the frequency of the A. C. I is 60 cycles per second, as shown at a in Fig. 6, whereas the generator 9, as shown in Figs. '7 and 8, has a speed of 1800 R. P. M. and its coils and poles are arranged to supply to the leads 8a, 8b, an alternating current of 60 cycles, but in which each alternation consists of two pulsations, as shown at bin Fig. 6, synchronized with an alternation of the same polarity in the other supplied current. As shown in Fig. 1, the leads 8a, 8b, are connected to the leads 4, 4a, to produce the alternating current c (see Fig, 6) supplied to leads 4, Ba, as later set forth.

As shown in Figs. '7 and 8, the generator 9 comprises a shaft l9 mounted in suitable bearings II provided in a housing I2. The shaft I8 is connected to and driven by a synchronous motor I0 (see Fig. l) to insure uniform rotation of the generator shaft I0, whereby the polarity of the A. C. generated by the generator 9 may be accurately maintained synchronized with that of the A. C. from the source 1. The motor I0 is preferably supplied with current by leads IE" from an outside source. The shaft II! supports four uniformly spaced poles I6, Ifia, IBb, IBc, surrounded by windings or coils I3, I341, I3b, I30, respectively, connected to rings I i which are engaged by suitable brushes I5, each winding being related to and surrounding the adjacent pole. As shown, all of the windings on the rotor poles are wound in the same direction. One terminal of the coil I3 is connected to one of the rings M; its opposite terminal being connected to the remote side of the coil I3a, whereas the opposite side of coil 13a is connected to the adjacent side of coil I317. The opposite side of coil I31) is connected to the remote side of the coil I30, the opposite side of coil I30 being connected to the other ring I l. The brushes I5 are connected by leads with a D. C. generator I'I, which driven by a motor H". The housing I2 supports four uniformly spaced coils or windings ll, ila, Ilb, We, each related to and surrounding a pole Ila: supported by the housing and insulated therefrom. As shown, all of the stator windings are wound in the same direction. As shown in Fig. 1, the coils Il, Ila, lib, Ilc, are connected by leads I8, IBa, to leads 9a, 813, respectively. The lead Ida is connected to one side of the coil I? and the lead from the other side of coil I? is connected to the remote side of coil Ila; the lead from the opposite side of coil Iia is connected to the adjacent side (right side as viewed in Fig. 8) of coil Nb; and the lead from the opposite side of coil I 1b is connected to the remote side of the coil l 10; whereas the other lead it is connected to the opposite side (upper side as viewed inFig. 8) of the coil IIc.

In this exemplified construction, the shaft I is driven at 1800 R. P. M., the rotor and stator poles are respectively spaced 90 and each pole has a width equal to poles of a generator for generating 180 cycles per second at this speed. Stated in another way, the stator has only one-third of the number of poles that would be required in a generator for generating 180 cycles per second at 1800 R. P. M., and if two additional poles were inserted in each space between each pair of adjacent poles, each pole having a winding connected in the armature circuit, the frequency of the generated wave would be 180 cycles per second. Since the poles in a 180 cycle generator would be separated by a space about equal to the pole width, the pole width of the generator of Figs. 7 and 8 is substantially one-sixth of the pole separation, or one-sixth the distance from the center of one pole face to the center of an adjacent pole face. The operation of the generator shown in Figs. 7 and 8 may be explained by reference to Fig. 14 which shows a development of the magnetic pole structures of the generator and the manner in which the windings are arranged on the pole pieces and connected together, so that alternate poles on the rotor have the same polarity and adjacent stator coils are connected in circuit in opposite directions. Assuming that the rotor in Fig. 14 is moving to the right, rotor pole IE moves from the center of stator pole Ila: past the side portion of the coil l1 surrounding the latter pole one pulsation of maximum voltage and current will be efiected such as pulse +b' in curve b of Fig. 6 and as this field or rotor Dole I 6 moves past the adjacent side portion of the next coil I 1a to the center of the stator pole, which is surrounded by said latter coil, a second pulsation of maximum voltage and current is effected, such as pulse +1)" in curve I) of Fig. 6, which pulsation is of the same polarity as the first pulsation +b' due to the fact that the latter coil Ha is wound or connected in the circuit in the opposite direction to that of the first coil I1, and because of the spacing and width of the stator and rotor poles the voltage and current will drop to substantially zero value during movement of the r0- tor pole relative to the space between the coils as shown by the dip in the curve 7) between pulses +1) and +1)" in Fig. 6. As pole I6 moves from the center of coil Ila into the space to the right of this coil, a negative pulse of maximum amplitude is generated as shown at b' in curve b of Fig. 6, and as pole l6 moves from this space between coils Ila and Ill) and reaches the center of coil llb, a second negative pulse of maximum amplitude is generated as shown at b" in Fig. 6. It will therefore be observed that in the movement of each field pole relative to two stator poles (that is, from the center of one stator pole to the center of the succeeding stator pole) one alternation of a cycle takes place and that two pulsations of the same polarity result in each alternation, and that each alternation in time interval equals the time interval of an alternation of the A. C. from the source 1. In other words, the time interval between the instant of start of pulse +13 an the instant of termination of pulse +b" is equal to one-half cycle of the alternating current wave from source 1 as represented in curve a, Fig. 6.

Accordingly, while the frequency of the A. C. from source 8 is similar to that of the A. C. from source 7, the pulsations in each alternation of the A. C. from source 8 reach their maximum voltage and current with a speed or time interval equal to 180 cycle A. C., and when superimposed on the A. C. 60 cycles, an alternating current as shown by curve 0 in Fig. 6 results.

As will be understood the windings l3, Ba, 1321, 13c and 11, Ha, l to, He, are wound, in relation to the speed of the shaft, to provide a predetermined output dependent upon the voltage of the source 1 and in relation to other units or devices connected in and forming parts of the system to produce the A. C. which is supplied to the transformer 3.

In my process I first supply an alternating current having a predetermined frequency from one source of supply and next I supply from a separate source of supply alternating current of the same frequency but having in each alternation a plurality of pulsations of the same polarity, each alternation of the current corresponding to and synchronized with one alternation of the same polarity in the first supplied alternating current. Accordingly, while in the last mentioned supplied current I provide a plurality of pulsations in each alternation, the polarity of each alternation is synchronized with an alternation having the same polarity of the first mentioned supplied current.

Finally, the separately supplied current is superimposed on the first mentioned supplied current to produce the welding current shown by curve 0 in Fig. 6. It will thus be seen that in the supply of the separate A. C. the pulsations in each alternation being effected with the speed of a 180 cycle A. C. and synchronized with an alternation of the first supplied A. C., the resultant alternation has a sustained voltage and current value between the first and last pulsations, the result being that the change from one polarity to the other polarity takes place in the minimum time.

In carrying out my process I may employ current at any predetermined frequency, but in my disclosure herein I have referred to A. C. 60

cycles as that is the usual frequency of the current supplied from outside sources. Therefore the source of A. C. supply 8 has a frequency of 60 cycles per second and follows a curve consisting of a plurality of pulsations in each alternation, but the change from one polarity of maximum voltage to opposite polarity of maximum voltage, and vice versa, is effected with the speed of A. C. having a higher frequency, whereas the source of A. C. supply 1 follows a sine curve and serves to build up the voltage and current value between the pulsations of the A C. from source of supply 8, whereby each alternation, between changes in polarity, has a sustained maximum voltage and current value.

It will be observed that I may provide for the supply of any desired quantity of current from source 8 for superimposing on the current supply from. source I by employing a generator constructed and wound to generate the desired quantity of current, but to reduce the cost of installation of the apparatus. I provide a relatively small generator the stator and rotor of which are provided with four uniformly spaced poles, each having a width corresponding to poles of a generator operating at cycles per second at 1800 R. P. M.

In this form of construction a small quantity of the current is supplied thereby and take from the source I the required additional quantity of current to supply the total current required in carrying out my process. Where the generator is driven at some other predetermined speed, the number of poles thereof will be increased or decreased.

Provision is made for steppin down or up the voltage of the current supplied from either of the sources I, 8, to the voltage of the current supplied from the other source, so that both currents will be at the same voltage when connected to the leads 4x, 42', which are connected to the opposite sides of the auto transformer 6; also, changes in voltage in both supplied currents to a predetermined voltage when found de-' sirable. 1 1 r In 1 and 2 the mains 4', 4a, are connected to the primary winding of a transformer IS, the terminals of the secondary winding thereof being connected to the-leads 4c, 4.1:. In

these arrangements, the transformer is wound to change the voltage of the A. C. source I to the same voltage of the current supplied from the A. C. source 8. For example, if the voltage of current supply 8 is 110 and the voltage of ourrent supply I is 220, the transformer I9 is wound to reduce this voltage to 110. In the modified arrangements shown in Figs. 1a and 2a, the leads 8a, 8b, are connected to the primary winding of a transformer No, the terminals of the secondary winding thereof being connected by leads 8a, 8b, to the leads 4x, 42:, respectively.

In Fig. 3, the mains 4', 4a, are connected to the primary winding of a transformer 21], the terminals of the secondary winding thereof being connected to the leads 41:, 42:. Also, the leads 8a, 8b, are connected to the primary winding of a transformer 2|, the terminals of the secondary winding thereof being connected to leads 80, 80', which in turn are connected to the leads 211:, 41:. In this arrangement the voltage of the currents from both sources I, 8, are transformed to an equal predetermined voltage. For example, if the desired voltage of current in leads 4x, 43:, is 110 and voltage of source I is 440 and the voltage of source 8 is 220, the transformers 20 and 2| are wound to reduce these voltages to 110. a

As shown in Fig. l, the lead 8a is connected to lead 43: and lead 8b is connected to lead 311;, leads Ga: and 42:, being connected to the opposite sides of the auto transformer 6. Fig. 2 shows a modified form wherein lead 4:1: is connected to one side of the auto transformer 8, lead film is connected to lead to and lead 8b is connected by lead 8d to the other side of the auto transformer 6. Fig. 4 shows a modification wherein the primary winding of a transformer is connected in each source of current supply as shown in Fig. 3. In this modification, one terminal of the secondary winding of transformer 20 is connected to the lead lr, the other secondary winding terminal being connected by a lead 80'' to one terminal of the secondary winding of the transformer 25, the other secondary winding terminal of the latter transformer being connected by leads 8c and 8d, to the lead Bx.

As will be observed from Figs. 1, la, 2, 2a, 3 and 4, the sources of current i, 8, may be connected in series or parallel relation.

Fig. 5 illustrates a. difierent modification. In this arrangement lead 4' of source 7 is connected to one terminal of the primary winding of a transformer 22 and lead do of source "l is contransformer 22 and the terminals of the sec ondary winding of the transformer 22 are connected by leads 8e, 8e, to the leads 4m, 4m.

23 indicates a suitable switch for connecting the sources of current supply to leads 4.134s.

From the foregoing description it will also be observed that by means of a suitable transformer or transformers connected to either or both sources of alternating current, the voltages may be transformed to a predetermined voltage for connection to the leads which are connected to the opposite sides of the auto transformer 6 or to the transformer 3, where some other means are employed in the system to regulate the voltage of the welding current.

Figs. 11 and 12 illustrate a modified form of generator construction wound to produce an alternating 60 cycle current wherein each alternation consists of three impulses of the same polarity, as shown in curve b (Fig. 13). In this form of construction the rotor 23 is mounted as shown in Fig. 7 and provided with four poles 24, 24a, 24b, 24c, uniformly spaced each pole having a width equal to each pole 25, 25a, 25b, 25c, of the stator, each of which has a width equal to a pole of a cycle generator driven at 1800 R. P. M. Each pole 24, 24a, 24b, 240, is surrounded by a coil 2 which is connected to the remaining coils and collecting rings similar to that shown in Fig. 8. The poles 25, 25a, 25b, 25c, are surrounded by inner coils 26, 26a, 26b, 260, respectively, which in turn are surrounded by outer coils 2'1, 21a, 27b, 270, respectively; also, between each side of the coils 28, 26a, 25b, 25c, and the adjacent side of the outer coil related thereto I preferably provide an additional pole preferably corresponding in width to each of the poles 25, 25a, 25b, 25c. These additional poles are indicated in Fig. 15 at 26', 26'', 26a, 26a", 26b, 28b", 26c and 260". The stator poles are equally spaced, and stator coils 21, 21a, 21b and 210 have common axes with coils 26, 26a, 26b and 260, respectively. The coils 26, 26a, 26b, 260, are connected similarly to the coils 11, Ha, lib, llc; likewise the coils 2?, 21a, 21b, 210, are connected in a similar manner; and preferably the sets of coils 26, 2611,2612, 26c and 21, 21a, 21b, 270 are connected in series as shown at 2B. In this arrangement, the lead 8a is connected to one side of a coil 210, the other side a thereof being connected to the adjacent side I) of coil 27b. The other sid b' of coil 27b is connected to the remote side 0 of coil 21a. The other side 0' of coil 21a is connected to the adjacent side 11 of coil 21, the opposite side d of coil 27 being connected to lead 26'. Lead 8b is connected to one side d of coil 26. The opposite side d of coil 26 is connected to the remote side c of coil 26a. Th opposite side 0" of coil 26a is connected to the adjacent side b of coil 26b. The opposite side b of coil 26b is connected to the remote side a of coil From the foregoing description, it will be understood that as each rotor pole 25, 25a, 25b, 25c, moves from the center of one stator pole to the center of the next stator pole it traverses those sides of the coils which are disposed between the two stator poles, the effect of which is to generate three impulses. For example, assuming the rotor is rotating clockwise, as viewed in Fig, 11, or is moving to the left in Fig. 15, rotor pole 24, in traversing the left side d of coil 26 will gen erate one impulse such as impulse +1) in curve b, Fig. 13 and as it traverses the sides 11, a, of coils 21, 210, it will generate a second impulse +b" and as it traverses the adjacent side a of coil 260 it will generate a third impulse +b", all of these impulses having the same example, positive); between the impulses the current will momentarily drop as shown at 11* (Fig. 13). As the rotor pole 24 moves from the center of pole 250 to the center of pole 25b, three impulses b, b" and b' of the same polarity (negative) will be generated. Accordingly, it will be observed that each alternation in each cycle consists of three pulsations or surges of the same polarity. The operation of the generator shown in Fig. 11 may be more clearly understood if it is observed that pulses b and b in curve b of Fig. 13 are the same as pulses b' and b" illustrated in Fig. 6 and generated in the st or windings of the generator shown in Fig. 7. The

middle pulse b' of Fig. 13, curve b, is generated each time a. stator pole passes from the last pole embraced in one of the stator coils in the 21 series to the first pole embraced in the next coil of the same series. All three pulses combine to produce a wave form like that shown in curve b oi Fig. 13. When an alternating current from source I as shown in curve a is combined with the current of curve b, the resultant current is shown in curve c oi Fig. 13.

To those skilled in the art to which my invention relates many changes in construction and widely difiering embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. My disclosures and the description herein are purely illustrative and are not to be in any sense limiting.

What I claim is:

1. A generator for generating alternating current at a predetermined frequency comprising a stator and a rotor each provided with poles of equal width and individual coils for the poles, thecoils for adjacent poles of the stator and the coils for adjacent poles of the rotor being oppositely connected and the poles of the stator being spaced to provide space between adjacent poles equal substantially to a multiple of the pole width, whereby the voltage generated in said stator coils drops to zero during movement of the rotor poles past the spaces between the stator poles.

2. A generator for generating alternating curpolarit (for.

rent comprising a stator provided with a plurality of equally spaced poles each carrying an individual winding, a rotor provided with a like number of wound poles and with the same spacing as the poles on the stator, adjacent coils on the stator and rotor poles being opp sitely connected in their respective circuits, said poles being spaced apart a distance to provide spaces between adjacent poles equal to at least twice the width of said poles, whereby the voltage generated in said stator coils drops to substantially zero during movement of the rotor poles past the spaces between the stator poles.

3. A generator for generating alternating current comprising a stator and a rotor each having uniformly spaced poles and individual coils therefor, the adjacent coils in said stator and rotor being reversely connected, the adjacent sides of adjacent coils of said stator being spaced apart a distance corresponding substantially to a multiple of the width of the face of the poles of said rotor, whereby the voltage generated in said stator coils drops to zero during movement of the rotor poles past the spaces between the adjacent sides of adjacent stator coils.

4. A generator for generating alternating current, comprising a stator and a rotor, each having uniformly spaced poles, individual coils for said stator poles, individual coils for said rotor poles, means for driving said rotor at a speed to generate an alternating current at a predetermined frequency, each of said poles of said stator and of said rotor having a width equivalent to that of a. generator operated at the same speed but designed to generate a current at a higher frequency equal to a multiple of said predetermined frequency, whereby is generated a wave at the predetermined frequency having a plurality of pulsations of one polarity only in each alternation.

5. A generator according to claim 4 wherein the width of the stator and rotor poles corresponds to a pole width which would be required to generate a current of a frequency equal to three times said predetermined frequency.

6. A generator comprising a stator and a rotor each having uniformly spaced poles provided with individual coils for generating current of a predetermined frequency when the rotor is driven at a predetermined speed, said stator poles with individual coils being spaced apart to provide a pole separation equal to a multiple of the pole width, two additional stator poles interposed between adjacent poles with individual coils, additional stator windings wound coaxially with said individual coils and embracing one additional stator pole on each side of each stator coil, said additional stator windings being connected in series with said stator coils, and adiacent windings being connected in opposite directions.

7. A generator of alternating current comprising a stator and rotor each having poles oi equal width, a series of poles on said stator being spaced apart by distances of the order of six times the pole width, and an individual coil on each pole of said series, adjacent coils in the series being oppositely connected in the generator circuit.

8. A generator according to claim 7 and including two additional stator poles positioned between each adjacent pair of poles with individual coils, additional stator windings wound coaxially with said individual coils and embracing one additional stator pole on each side 01' each stator coil, said additional stator windings being connected in series with said stator coils. and

. adjacent windings being connected in opposite directions.

HOWARD I. MORRIS. 

